The measurement of propagation delay in multimode optical fibre with pulse-reflection-oscillation method

Using the pulse-reflection-oscillation method, a high precision optical fibre propagation delay measurement system is made and applied to measure multimode optical patchcords of four different lengths (10, 20, 50 and 100 m). The result shows that the standard deviation is less than 11 ps.     

Corner flow of a suspension of rigid rods

Stress singularities in the neighbourhood of sharp corners can be a source of severe problems in the numerical simulation of non-Newtonian flows leading to loss of convergence with grid refinement (G.G. Lipscombe, R. Kennings and M.M. Denn, J. Non-Newtonian Fluid Mech., 24 (1987) 85 [1]). For Newtonian flows the nature of this singularity is given by the analysis of Dean and Montagnon (W.R. Dean and P.E. Montagnon, Phil. Trans. R. Soc. London, Ser. A., 308 (1949) 199 [2]) in terms of similarity solutions. In this paper we extend this similarity analysis to a suspension of rigid rods. In the limit of nearly full extension the FENE constitutive model has the same behaviour as such a suspension. Our analysis predicts the possibility of lip vortices but their behaviour is somewhat inconsistent with those observed experimentally.     

ELECTROSTATICALLY SUPPORTED MIXING OF FINE GRAINED PARTICLES

The processing of fine-grained particles with diameters between 1 and 10 microns is difficult due to strong van-der-Waals attraction forces. In order to improve the handling properties, the fine-grained particles, i.e. host-particles,are coated with various nanoparticles, i.e. guest-particles. The mixing of fine-grained powders is influenced by particle-particle interactions. If these forces are distinctively used, both interactive and ordered mixtures can be produced.These particle mixtures consist of composite-particles that have new physical properties. These modified properties d epend strongly on the coating process, the diameter- and mass-relationship of the guest- and the host-particles. The properties of the composite-particles can systematically be adjusted to the requirements of industrial applications. For example, a laboratory bubbling fluidized bed can be used to describe the conveying behavior of the functionalized host-particles. Applications for the functionalized particles are in the pharmaceutical and the powder coating industries,e.g. enhanced dry powder inhalers and thin lacquer films. The present research compares three different mixing/coating processes. The composite-particles are characterized by TEM, SEM and with their fluidization characteristics. The coating process itself is monitored by the electrostatic charge of the particles.     

大麦花药培养及其胚性悬浮细胞系的高频快速建立

研究了（1）在低温预处理过程中，不同相对湿度对大麦花药出愈率的影响；（2）低温处理愈伤组织对植株分化的影响；（3）高频快速建立大麦胚性悬浮细胞系，结果表明，低温预处理的较大相对湿度能明显促进花药的出愈率，低温处理愈伤组织能提高绿苗率，以7周龄的花药胚性愈伤组织为起始材料高频快速建立了均质，分散性好的胚性悬浮细胞系，建立频率约为25%～50%，已8～9周龄的花药胚性愈伤组织作为起始材料，难以建立胚性悬浮细胞系。     

Interpretation of relaxation and swelling phenomena in lyocell regenerated cellulosic fibres and textiles associated with the uptake of solutions of sodium hydroxide

The uptake of solutions of sodium hydroxide by lyocell fibre results in a phenomenon in textiles described as swelling–shrinkage. The response of woven fabrics in a tensile stress–relaxation experiment shows two time-dependent processes, corresponding to different mechanisms of pressure development. Rapid diffusion has been assigned to osmotic swelling through the interconnected pore structure of the fibre (D = 6–15 × 10⁻¹² m²/s), which is influenced by the extent of ionization of hydroxyl groups at the pore surfaces. A ratio for the cellulose and water dissociation constants (K_cell/K_w) of 70 provides best agreement with experimental data. A second slower diffusion process (D = 2–10 × 10⁻¹⁴ m²/s) is assigned to transport through the cellulose polymer structure, associated with the Na-cellulose transition. This can be modeled assuming an ion-exchange equilibrium, where the cellulose gel converts reversibly between compact hydrogen and expanded sodium forms, with K = 1.04 × 10¹⁴, in favour of the hydrogen form. The model successfully predicts the concentration dependence of the transition and the movement to higher concentration with external constraint. The slow diffusion process only becomes apparent at high alkali concentrations, as the pores in the fibre collapse due to the expansion of the gel. Continued gel-diffusion is only possible through the polymer phase, which then dominates over fast pore-diffusion.     

Effects of the degree of surface modification on the rheological responses of precipitated silica suspensions in benzyl alcohol

Two types of precipitated silica powders modified by poly (dimethylsiloxane) (PDMS) were suspended in benzyl alcohol and their rheological properties were investigated as a function of silica volume fraction, φ. The suspensions were classified into sol, pre-gel, and gel states based on the increase in φ. An increase in the degree of surface modification by PDMS caused gelation at higher φ. Plots of apparent shear viscosity against shear rate in the sol and pre-gel states of highly modified silica suspensions showed weak shear thickening behavior, while the same plots for silica suspensions with a low modification level exhibited shear thinning behavior. The dynamic moduli of hydrophobic suspensions in the pre-gel and gel states were dependent on the surface modification: the storage modulus G′ was larger than the loss modulus G″ in the linear region and these moduli increased with increasing φ, irrespective of the silica powder. The linear region of the φ range for the precipitated silica suspensions was wider than that for the fumed silica powders modified by PDMS suspended in benzyl alcohol, while the G′ value in the linear region for the precipitated silica suspensions was less than those for the fumed silica suspensions.     

Dynamic-mechanical properties as a function of luffa fibre content and adhesion in a polyester composite

In this work, the characteristics of a vegetable fibre (luffa cylindrica) polyester composite are studied as a function of fibre surface treatment (with NaOH, Ca(OH)₂ and silane) and fibre content (30%, 40% and 50%). Composites were prepared through compression moulding and characterized with thermogravimetric and dynamic-mechanical analyses. Higher storage modulus was obtained with Ca(OH)₂ treated composites, reaching nearly 70% increase. Higher loss modulus (E”) was noted in for silane treated fibre (at 50%) and a high peak in damping factor was noted for Ca(OH)₂ treated fibre (at 50%). Cole-cole plot showed highest homogeneity for the Ca(OH)₂ treated composites. Electron microscopy revealed the fracture modes in static tested composites. The general properties obtained indicate that the composites can only be used for low loading applications.     

Preparation of stable colloidal suspensions of superdisintegrants via wet stirred media milling

Superdisintegrants are cross-linked polymers that can be used as dispersants for fast release of drug nanoparticles from nanocomposite microparticles during in vitro and in vivo dissolution.Currently available superdisintegrant particles have average sizes of approximately 5-130 μm,which are too big for drug nanocomposite applications.Hence,production of stable superdisintegrant suspensions with less than5 μm particles is desirable.Here,we explore the preparation of colloidal suspensions of anionic and nonionic superdisintegrants using a wet stirred media mill and assess their physical stability.Sodium starch glycolate(SSG) and crospovidone(CP) were selected as representative anionic and nonionic superdisintegrants,and hydroxy propyl cellulose(HPC) and sodium dodecyl sulfate(SDS) were used as a steric stabilizer and a wetting agent/stabilizer,respectively.Particle sizing,scanning electron microscopy,and zeta potential measurements were used to characterize the suspensions.Colloidal superdisintegrant suspensions were prepared reproducibly.The extensive particle breakage was attributed to the swelling-induced softening in water.SSG suspensions were stable even in the absence of stabilizers,whereas CP suspensions required HPC-SDS for minimizing particle aggregation.These findings were explained by the higher absolute(negative) zeta potential of the suspensions of the anionic superdisintegrant(SSG) as compared with those of the nonionic superdisintegrant(CP).     

First seconds in a building's life-in situ synchrotron X-ray diffraction study of cement hydration on the millisecond timescale

Setting cement: highly dynamic hydration processes that occur during the first seconds of cement hydration were studied by time-resolved synchrotron X-ray diffraction. Polycarboxylate ether additives were found to influence the formation of the initial crystalline hydration products on a molecular level.